If you were one of the many people that upgraded to a new iMac back in May when they got new hardware you aren't alone. We reviewed the new iMac when it launched. The machines got new processors and larger storage drives. If you opted for one of the iMacs that had a 1TB HDD from Seagate inside you may need a new HDD. Some of those early iMacs had an issue with the 1TB HDD and Apple is looking to replace those drives for you.
Apple has said that the HDDs could fail under certain conditions and that the issue only affects a very limited number of machines. The iMac had to be purchased with the Seagate 1TB HDD between May 2011 and July 2011 and the issue affects both the 21.5-inch and the 27-inch iMac computers. Apple is contacting owners of affected machines that provided a valid email address when registering.
If you didn’t provide a valid email or think your machine might be covered, you can hit the replacement page on Apple's website and enter your serial number to see if your machine is affected. The replacement offer for the HDD will last through July 23, 2012. The coverage for the HDD doesn't extend the standard warranty on the iMac. Apple also won’t back up your current HDD for you.